Organic Light-Emitting Diodes (OLEDs) are solid-state lighting devices that are very different from conventional LEDs both in terms of physical appearance and in terms of performance characteristics. OLEDs are larger in surface area but much thinner than LEDs. OLEDs are lower in luminance and produce light which is more diffuse in appearance. The physical nature of OLEDs allows them to be used in ways that are impossible with conventional LEDs. OLED panels can be manufactured that are so thin and lightweight that they are flexible/foldable and can even be rolled up and then unrolled. These panels can be mounted flush onto a curved surface. It is even possible to manufacture OLED panels that are transparent. These transparent panels are currently at the bleeding edge of the technology, and still very much under development with no actual commercial products in sight right now. However, this would allow them to be used in unique ways that have never been possible with any previous lighting product. For example, in theory one could build an OLED light panel into a window pane. During the day time, the window would be transparent and allow people to look out, but then at night, the OLED panel could be powered on to cause the window pane itself to emit light into the room. Clearly, there is enormous future potential from this technology, however there are currently two major problems that require further development work. Those problems are longevity and a definite need for more reliable, optimized, and efficient drivers
OLEDs degrade very quickly when exposed to either oxygen or moisture in the environment. For this reason, most LED panels are currently built such that the OLEDs are sandwiched between either a layer of metal and a layer of glass or two layers of glass which are then totally sealed around the edges with epoxy. When flexibility of the final panel is desired, thin sheets of a flexible but highly resilient plastic called polyethylene terephthalate are used to create the sealed envelope that will contain the OLEDs. Typically, a desiccant material is also placed into the sealed envelope along with the OLEDs to absorb residual moisture. Any failure of the environmental seal will significantly shorten the lifespan of the panel, and can cause dark spots within the OLED panel that grow over time. At this point, OLED light panels are being built in small quantities just for use in development and testing of the technology. The fact that the panels are physically fragile will need to be addressed before OLEDs can start being built into general purpose luminaires, an application where they will be expected to survive a reasonable amount of rough handling.
OLED panels experience a phenomenon known as voltage rise over the life of the panel. What this means is that as the OLED panel ages, the drive voltage necessary to produce the same level of light must increase over time. This voltage rise phenomenon occurs in addition to the normal luminance decay phenomenon which causes the light output to decline over time. Luminance decay does affect OLED’s just the same as conventional LEDs. These factors make it somewhat more difficult and complex to build drivers for OLEDs. The overall energy efficiency of OLED lighting is currently still significantly lower than LEDs, and there is a lot of room for optimization and improvement of the OLED drivers. In terms of luminous efficacy, which is lumens produced per watt of energy consumed, LEDs are still about 2.5 times more efficient than OLEDs. However, as this technology continues to be developed, there will certainly be significant improvements made in energy efficiency.
OLED lighting is a technology that is still under development, and not yet ready for the marketplace. It will likely be a few more years before we begin to see luminaires for sale that feature OLEDs. For the moment, the principal development work will continue to focus on improving energy efficiency, improving the lumen maintenance over time, and increasing both the physical robustness and the lifespan of the OLED panels. Once these present limitations of the technology have been overcome, OLEDs will surely become a contender in the general purpose lighting arena.